Sound Jitter on timeline not trimmer window

Hello
Im new to this forum and to Vegas movie studio HD 10 but not new to vid editing.
im have a problem with the sound
When i play the vid file in the trimmer window the sound is fine not a propblem but as soon as i move it to the timeline i get jitter and the sound jumps about all over the place you can see in the sound waves, The trimmer one is all as it should be but when its in the timeline it is quite flat and big jumps here and there.
Any ideas everything else is perfect and it only does it on some files even though there off same HD panasonic camcorder or just music files imported
Thanks
MArk